Not even PDFs are safe when it comes to securing a machine, it seems. A British security researcher has revealed information about certain flaws he discovered
in Adobe Reader
and PDFs, several of which could lead to system compromise and affect even the latest patched version of the program. One of the exploits can force the computer in question into opening any webpage, perhaps one that further exploits an unpatched flaw in a browser. Of course, the majority of these revolve around the user trusting a document they receive or at least trusting an online PDF to be safe. If you're using an alternative reader, you may not be as vulnerable, though the article did not mention anything of this. Interesting read.